Epinephelus coioides, a kind of marine coral reef fish, belongs to Serranidae family. For Epinephelus genus, the commercial market is stable and the price thereof is costly. Further, E. coioides is one of the marine fish whose artificial reproduction and breeding technology is the most difficult, and hitherto, the supply of breeding fry has depended on catching the wild juveniles. In the recent years, the large scale artificial reproduction of E. coioides has been developed in Japan, the countries in Southeast Asia, China, Taiwan and the coast of South China. With the development of large-scale artificial reproduction technology for marine fish, nature fries has not been sufficient to satisfy the need of culture production, and the artificial breeding technology has become the key technology for its continuous development. Although some primary studies on reproduction biology have been made, the basis of artificial breeding and regulation of reproduction is only very poorly understood. According to the statistics of 2000 by Qiyong ZHANG et al (QiYong Zhang and WanShu Hong, Status and perspects of artificial propagation and breeding technique of marine fish in China in 1990s. Modern fisheries information, 2000, 15(3):3–6), the Epinephelus species whose fry has been successfully cultivated in China include E. akaara, E. fario, E. malabaricus, E. coioides and the like. However, the yields obtained actually are far from the goal of stable fry batch production.
Difficulties in artificial reproduction and breeding of E. coioides may include the following: (1) E. coioides is hermaphroditic, the female matures first, then sex transformation occurs; (2) the quality of zygotes is not good and the hatching rate is low; (3) fry individuals are tenuous and captious to the bait. There are also other problems, for example, cannibalism behavior between the larvae and the juveniles, diseases, and the like. In particular, the “female to male” sex transformation process in the individual development of E. coioides means that the male parents are all aged, and are generally above 6 years old. The result is a relatively low proportion of juveniles in any population and bait rapidly depleted by the non-reproducing individuals. Even if male parents are caught, the fertilization rate is still very low because the sexual maturity of male and female parents is not synchronous. The present method of fry breeding is to feed, inject or imbed the heterogenous sexual steroid hormone (17a-Methyl-testosterone) to force a sex-reversal of the cultured male parents. However, the molecular mechanism of sex reversal is poorly understood, and administrating greater amounts of heterogenous steroid hormone may have disadvantages. For example, labor and time may be wasted, sea were polluted, the effectiveness of sex transformation may be poor, male sperms are weak after sex transformation, and when administration of the hormone is stopped, sex reversion occurs. Fish treated by imbedding the hormone may not take food or may take little food, and thus is detrimental to their normal development.